User equipment configured to provide synchronization information for sidelink D2D communications using allocated resource units

ABSTRACT

A signal structure for use in D2D communications is described. In one embodiment, a preamble for automatic gain control at the receiver end is included in the transmitted signal. Techniques for scheduling of D2D transmissions using carrier sensing multiple access (CSMA) and a power control schemes for interference management are also described.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/261,439, filed Sep. 9, 2016, which is a continuation of U.S. patentapplication Ser. No. 13/729,164, filed Dec. 28, 2012, now issued as U.S.Pat. No. 9,661,658, which claims the benefit of priority under 35 U.S.C.119(e) to U.S. Provisional Patent Application Ser. No. 61/624,185, filedon Apr. 13, 2012, each of which is incorporated herein by reference inits entirety.

BACKGROUND

Device-to-device (D2D) communications is one means for improving theperformance of LTE (Long Term Evolution) and other cellular networks. InD2D communications, terminals (referred to as user equipments or UEs inLTE) communicate with one another directly rather than being linkedthrough the base station (referred to as an evolved node B or eNB inLTE). D2D communication between two or more D2D devices is typicallyvery local, due to the short distance between D2D devices and uses verylower transmit power. D2D communications is also a powerful way toincrease spatial reuse in cellular systems for higher throughput.

One approach to D2D communications as an underlay to an LTE networkinfrastructure is an out-of-band solution, in which the D2D traffic isunloaded to an unlicensed band (e.g., Wi-Fi as defined by the IEEE802.11 standards) on the application layer. Another approach is anin-band solution, in which the D2D transmissions take place in the samelicensed band used by the LTE network. The present disclosure deals withaspects of the in-band approach to D2D communications. In particular,the focus is on a signal structure for supporting in-band D2Dcommunications, scheduling of D2D transmissions, and power control forinterference management.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows example UE devices for D2D communications and an eNB.

FIG. 2 illustrates a signal structure for D2D communications in oneembodiment.

FIG. 3 shows the operation of an AGC in a D2D receiver in oneembodiment.

FIG. 4 shows an example algorithm performed by the D2D receiver inaccessing the channel via CSMA.

FIG. 5 illustrates an example of numbering designations used for D2Dslots distributed in time and frequency.

FIG. 6 is a diagram illustrating a problem with CSMA when transmissionpowers vary among D2D devices.

FIG. 7 shows the operation of an auto-correlator bank for detectingtransmit power from the preamble.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific embodiments to enable those skilled in the art to practicethem. Other embodiments may incorporate structural, logical, electrical,process, and other changes. Portions and features of some embodimentsmay be included in, or substituted for, those of other embodiments.Embodiments set forth in the claims encompass all available equivalentsof those claims.

FIG. 1 shows an example of a UE 10 and a UE 20, each of whichincorporates a processor 21 interfaced to a radio-frequency (RF)transceiving circuitry 22 that is connected to one or more antennas 23.A base station or eNB 40 is shown with a processor 41interfaced to an RFtransceiving circuitry 42 that is connected to a plurality of antennas43. The illustrated components are intended to represent any type ofhardware/software configuration for providing air interfaces for bothLTE and D2D communication and for performing the processing functions asdescribed herein. In the embodiment shown in the figure, UEs 10 and 20both communicate with the eNB 40 via LTE links and with one another viaD2D link.

The physical layer of LTE is based upon orthogonal frequency divisionmultiplexing (OFDM) for the downlink and a related technique, singlecarrier frequency division multiplexing (SC-FDM), for the uplink. InOFDM/SC-FDM, complex modulation symbols according to a modulation schemesuch as QAM (quadrature amplitude modulation) are each individuallymapped to a particular OFDM/SC-FDM subcarrier transmitted during anOFDM/SC-FDM symbol, referred to as a resource element (RE). An RE is thesmallest time-frequency resource in LTE. LTE also provides for MIMO(multi-input multi-output) operation where multiple layers of data aretransmitted and received by multiple antennas and where each of thecomplex modulation symbols is mapped into one of the multipletransmission layers and then mapped to a particular antenna port. EachRE is then uniquely identified by the antenna port, sub-carrierposition, and OFDM/SC-FDM symbol index within a radio frame. LTEtransmissions in the time domain are organized into radio frames, eachhaving a duration of 10 ms. Each radio frame consists of 10 sub-frames,and each sub-frame consists of two consecutive 0.5 ms slots. Each slotcomprises six indexed OFDM symbols for an extended cyclic prefix andseven indexed OFDM symbols for a normal cyclic prefix. A group ofresource elements corresponding to twelve consecutive subcarriers withina single slot is referred to as a resource block (RB) or, with referenceto the physical layer, a physical resource block (PRB). Each PRB pairconsists of two slots sequential in time.

In the case of FDD (frequency division duplex) operation, where separatecarrier frequencies are provided for uplink and downlink transmission,the above-described frame structure is applicable to both the uplink anddownlink without modification. In TDD (time division duplex) operation,subframes are allocated for either uplink or downlink transmission witha special subframe occurring at the transition from downlink to uplinktransmission (but not at the transition from uplink to downlinktransmission). The eNB manages the allocation of uplink and downlinksubframes within each radio frame during TDD operation.

D2D Signal Structure

With in-band D2D communications, UEs acting as D2D devices maycommunicate using time-frequency resources allocated for the D2D link bythe eNB. Timing and synchronization is then done as in a conventionalLTE link where each D2D device synchronizes its clock and symbol/slotboundary with the eNB as the conventional UE. Since D2D communicationsare usually within a short distance, the propagation time from the sameeNB to the communicating D2D devices should be roughly the same. Moreprecisely, the difference between the two timings (e.g. the symbolboundaries) of the communicating D2D pair should be around 0.2-1 μs,which is within the cyclic prefix of OFDM or SC-FDM, obviating the needfor additional synchronization mechanisms. Although the timing andfrequency synchronization can be achieved as in the conventional system,there are still additional aspects for D2D communications. There may bedifferent eNBs such as macro eNB and pico eNB deployed in the area ofthe D2D devices. The eNBs from different operators may not synchronizeeach other or have the same OFDM symbol duration. Therefore, the timeand/or frequency reference for the communicating D2D devices has to bespecified. For example, the communicating D2D devices may associate withthe same eNB and that eNB specifies an eNB e.g. a macro or a pico eNBfor the synchronization. In addition to the timing and frequencysynchronization, other physical and MAC layer parameters such as carrierfrequency, bandwidth, cyclic prefix length, group ID, and D2Dfrequency-time resource are all needed to be specified by an eNB or aD2D coordinator or D2D group owner. Using time-frequency resources asallocated by the eNB, there are two modulation options for D2D datamodulation, OFDM and SC-FDM, which are employed for the downlink anduplink in a conventional LTE device, respectively. The two schemes sharemost of the hardware components such as those for performing the FFT(fast Fourier transform) and IFFT (inverse fast Fourier transform).Although SC-FDM suffers less from a high PAPR (peak-to-average powerratio) than OFDM, it may still be desirable to use OFDM for D2D. First,since D2D communications is for short range, and its peak power shouldbe much less than that of the conventional uplink transmission. Second,SC-FDM suffers from inter-symbol interference (ISI) while OFDM does not.Third, the channel training overhead is less for OFDM than SC-FDM.

In order for a D2D receiver to demodulate a received signal, a channeltraining signal is needed. For lowering the complexity of a UE that isalso configured for D2D operations, the existing reference signal (RS)patterns used in LTE such as UE-RS or DM-RS may employed for D2D aswell. However, the channel characteristics such as multipath delay andtime variation are quite different for a D2D link compared with atypical LTE link. D2D devices are usually indoors and experience lessmobility and delay spread than conventional UEs. Therefore, the RSdensity for the D2D link may be made smaller than that of a conventionalcellular link, and reducing the RS density improves the throughput.Since either OFDMA or SC-FDM could be used for D2D communications,somewhat different channel training designs could be used for each. ForOFDM, the channel training signal should be a set of referencesubcarriers, which may a subset of the existing RS pattern. For example,with respect to a conventional LTE RB, only the existing RSs of thefirst slot of a PRB pair could be used for channel training with the RSsin the second slot used for data. Besides taking a subset from theexisting RSs, a different RS pattern may be used. For example, the RSsubcarrier may be only located at the first OFDM symbol of the PRB pairfor reducing channel estimation latency and channel training overhead.For SC-FDM, the channel training signal should be one or multiplereference symbols solely occupying the frequency band or the sub-band ofthe PRB during the symbol duration. Again, fewer RSs may be used for theD2D link than in a conventional LTE uplink RB, e.g., the second RSsymbol in the RB may be replaced by a data symbol.

In conventional LTE communications, a UE only communicates with the eNBover both the downlink and uplink. This allows both the timing and powerlevel to be controlled via various control channel signals between theeNB and the UE such as ranging and power control feedback. The situationis different in the distributed D2D case. Since one D2D device mayreceive signals from different D2D devices, the received power willtypically vary from device to device. When a UE receives a signal over aradio frequency (RF) carrier, the signal is downconverted to baseband,amplified, and then digitized with an analog-to-digital converter (ADC)before being demodulated. Accurate digitization of the received signal,however, requires that the gain of the amplification be such that theresulting amplified signal will fall within a proper range of the ADC.For setting the AGC, a short preamble may be placed at the beginning ofthe transmission. This short preamble should be located at the samefrequency band or sub-band as the subsequent data signal. The shortpreamble may comprise multiple periods of the same signal in the timedomain, where the repetition of the same signal enables detection of thepreamble via autocorrelation. The duration of the short preamble may be,for example, between 0.5 and 20 μs.

Due to the small payload size of sensors, which may be the main part ofD2D devices, 1 slot×1 RB can be defined as the basic resource allocationunit, referred to herein as a D2D slot or D2D packet. For large payloadsize the basic resource allocation unit can be 2 slot×1 RB. An exampleof a signal structure for a D2D packet 200 incorporating the featuresdescribed above for SC-FDM is as shown in FIG. 2. Following the shortpreamble SP and a reference signal RS, are the SC-FDM symbols forcarrying control information or data, which are carried by resourceelements mapped to a physical D2D control channel (PdCCH) or a physicalD2D shared channel (PdSCH), respectively. A D2D packet for OFDM would besimilar except that the reference signals would be specific resourceelements distributed in time and frequency. The cyclic prefixes of theOFDM or SC-FDM symbols may be made shorter than those used in thecellular LTE link. FIG. 3 illustrates the operation of a D2D receiverutilizing the short preamble of the D2D packet. After reception of theRF carrier signal by the RF transceiver 301, the resulting signal isdownconverted to baseband by downconverter 302, amplified by amplifier303, sampled and digitized by ADC 305, and then demodulated byOFDM/SC-FDM demodulator 306 to extract the transmitted symbols. Prior todigitization, automatic gain control module 304 detects the shortpreamble at the beginning of a D2D packet and, based upon the power ofthe signal, adjusts the gain of amplifier 303.

Distributed Scheduling Control

Within the in-band approach to D2D communications, there are basicallytwo alternative techniques for scheduling transmissions. One relies onthe base station, the eNB, to schedule and coordinate the D2Dtransmissions using the allocated time-frequency resources. The othertechnique mainly relies on the D2D devices themselves to contend fortransmissions using those allocated time-frequency resources as well asmanage any interference. The second technique is most suitable forsensor networks, which typically have small size packets but a largecontrol overhead. For such small packets, scheduling and interferencecontrol by the eNB may be inefficient for at least two reasons. First,there will be a large number of D2D devices and links, and the eNBcannot be totally aware of the interference status between any two D2Dlinks. And even if the eNB can ask D2D devices to report theinterference measurements, the system may not be able to afford thelarge feedback overhead from those reports or the large control overheadin scheduling so many D2D transmissions.

In the technique for distributed scheduling control described here,carrier sensing multiple access (CSMA) is used for in-band D2Dcommunication. The CSMA not only achieves high spatial reuse but alsoreduces the control overhead between the D2D device and the eNB. Asdiscussed earlier, the resources for D2D communications are allocated bythe eNB. The eNB broadcasts the resource allocation to a group of D2Ddevices. The grouping of the devices may be according to the qualitiesof the channels between them. As described above, the resources may bedivided into D2D slots or PRB pairs, where a group of allocated D2Dslots or PRB pairs may be localized in time or/and frequency or may bedistributed in frequency and time. In one embodiment, each such D2D slotis used as a time slot for slotted aloha-type CSMA incorporating aback-off mechanism to reduce collision frequency. The steps involved inan example algorithm are as shown in FIG. 4 for a D2D device that wishesto transmit. At step 401, the device randomly selects a number N tobegin a countdown. At step 402, the device senses the beginning of thenext D2D slot. If the slot is busy, the countdown is suspended at step403 and step 402 is repeated. If the slot is not busy, N is decrementedat step 404. If it is determined that N has been decremented to zero atstep 405, the device transmits at the next slot at step 406. Otherwise,the device returns to step 402. The D2D slots may be labeled insequential order as illustrated in FIG. 5 so that the countdown of slotswithin the back-off window can be conducted. The order of the slots inFIG. 5 is frequency first for reducing the delay and taking the halfduplex operation of a D2D device into account.

In another embodiment, a transmitting D2D device may specify areservation time in the PdCCH of a transmitted packet to indicate howlong the device is to be transmitting. By detecting the reservation timespecified in the PdCCH, D2D devices can skip the operation of carriersensing and go to sleep state until the reservation time runs out. Thisreduces the power consumption of the D2D devices. Also, since the delayof aloha-type CSMA is unbounded, another embodiment involves using theeNB if needed to fulfill latency requirements. For example, the D2Ddevice can ask the eNB to forward the D2D data to the destination D2Ddevice if the D2D link cannot send the data out in time. This improvesthe latency of the D2D traffic by using eNB as a backup.

Power Detection and Control for Interference Management

In the D2D system as described above, multiple D2D devices may contendfor channel access and send data to other D2D devices. Since a D2Ddevice may transmit data to different D2D devices at differentdistances, the transmission power should be varied according to thetransmission distance for the purposes of reducing interference,increasing spatial reuse, and optimizing power efficiency. In a D2Dnetwork with a large number of nodes, carrier sensing multiple access(CSMA) such as described above is the most efficient way for channelaccess control. However, CSMA alone cannot support fair access amongnodes with different transmission powers. The reason is that, a devicecan no longer predict its interference level at another device using thereceived signal from the conventional carrier sensing. For example, asillustrated in FIG. 6, node C would like to transmit and doesn't want tointerfere with any existing transmissions on the air. Node C doescarrier sensing and detects the existing transmission from node A tonode B. In conventional CSMA, if the received signal power detected fromthe carrier sensing is below a certain threshold, node C should considerthe channel idle and may access the channel. The assumption here,however, is that the interference level is reciprocal between anytransmitter and receiver pair. If a receiver experiences an interferencelevel from a transmitter, the transmitter should experience the sameinterference level when the original transmitter listens to the originalreceiver's transmitter. This relies on the fact that the wirelesschannel is reciprocal and the transmission power is constant among allnodes. However, when the transmission power varies across nodes, thisassumption is no longer true. In the example in FIG. 6, node A and nodeB are close to each other, node A uses low power to talk to node B. Theresultant interference from node A to node C is small because of thereduced transmission power. Therefore, if node C does not know that nodeA reduced its transmission power, node C may start transmitting withfull power to talk to node B.

A solution to this problem involves specifying the transmit power levelbefore the transmission so that the other nodes can predict theinterference level. The transmit power level may be sent or broadcastedin a (D2D) control channel by the transmitter node or a coordinatornode. Instead of using a control channel, which may be able to containmultiple types of control information, the transmit power level can besimply specified by a transmission power indicator added to the D2Dpackets. The advance specification of the transmission power before theactual transmission can be applied to CSMA and other types of mediumaccess such as distributed scheduling. Since the transmit power level isfor other nodes to predict their interference level in case they causeinterference problems, this advance specification needs to be sentreliably. For example, high power transmission or reliable encoding suchas repetition, spreading, and channel code may be applied forbroadcasting the transmit power level. In a carrier sensing type ofmedium access, a D2D receiver wishing to transmit may then use thetransmission power information for transmission power estimation duringcarrier sensing. In one embodiment, the transmit power level is signaledat the beginning of each transmission burst. After the transmit powerlevel is detected or estimated, the path loss can be estimated bysubtracting the received signal power from the transmitted power. Usingthe estimated path loss, the D2D receiver can decide if it can transmitand what transmit power level should be used. Described below areexample techniques for transmitting the transmission power indicator.

In one embodiment, D2D packets with different transmission powers may besent with different preamble sequences, where the sequence can bedetected during the carrier sensing or during channel estimation. Asdescribed above, the D2D packet preamble may be also used for settingthe adaptive gain control (AGC) or for channel estimation. For example,short preambles with different periods (e.g. 2 μs, 3 μs, or 5 μs) can beused for signaling the transmit power level and setting the AGC. Thereceiver can have a bank of auto-correlators with different correlationdurations (e.g. 2 μs, 3 μs, or 5 μs) for detecting the signal arrivaland transmit power level. An example of an auto-correlator bank in a D2Dreceiver used to distinguish between preamble periods of 2 μs and 3 μsis shown in FIG. 7. After reception by the RF transceiver 301 anddownconversion to baseband by downconverter 302, versions of the signaldelayed by 2 μs and 3 μs are produced by delay elements 320 and 330,respectively. The delayed versions of the signal are then correlatedwith the undelayed signal by correlators 310 and 311. The outputs of thecorrelators are then compared by comparer 312 to detect the periodicityof the preamble.

In another embodiment, rather than putting the transmit power indicatorin the preamble sequence, the transmit power indicator (TPI) may be putin the channel training signals if one prefers using digital samples.For example, the TPI may be placed in the reference signals such as asingle SC-FDM symbol used as the RS in SC-FDM or in the differentresource elements used as reference signals in OFDM. A different channeltraining sequence can be applied for each different transmit powerlevel. Since the number of power levels may be between four and eight,only a handful of sequences may be needed, and sequence detection errorwould be negligible at the operating SNR of the data frame. Fordistributed reference signals such as in OFDM, the transmission powercan be detected during the entire D2D packet as compared to the otheroptions. If the listener to the channel misses the beginning of the D2Dpacket, it can still learn about the transmission power later using thedistributed reference signals.

If the number of transmit power levels is relatively large, the previousapproaches may incur a high error rate in the sequence detection. Inanother embodiment to deal with this problem, the transmit power levelcan be signaled by the bits in the physical layer header. The physicallayer header may follow the sequence for setting the AGC such as theshort preamble. This reduces the latency of carrier sensing and thereceiver power consumption. The receiver should decode the TPI bits fromthe header. The header may have CRC check bits to verify the detectedTPI bits. As discussed above, besides the transmission power, thereceiver may be also interested in the duration of the transmission forenabling collision avoidance. Such duration information, or channelreservation time, can be also in the header or implicitly specified bythe system. In an example of an implicit specification, the duration maybe always one subframe for some system.

In another embodiment, the transmission power level is signaled bychannel reservation exchange before the data block transmission. Thiswould be similar to the RTS/CTS channel reservation used in Wi-Fi. Incellular D2D, the channel reservation can be done by the transmitter andreceiver with a default (high) power level such that other D2D devicesin the vicinity can know about the reserved duration and thetransmission power within the duration. As an alternative, the basestation may broadcast the channel reservation and transmit power levelto nearby D2D devices for a transmitting pair.

Example Embodiments

In one embodiment, a UE comprises a radio transceiver to provide an airinterface for communicating with an eNB and for D2D communications andprocessing circuitry connected to the radio transceiver to: receiveallocations of time-frequency resources for D2D communications from theeNB and establish a D2D communications session with a second UE. Wherethere are multiple eNBs, the processing circuitry may be to establishtiming and frequency synchronization with the same eNB as the second UE.The resources or D2D transmissions to and from the second UE may be thesame resource structures as used in a cellular LTE link or may beorganized into D2D slots with each D2D slot beginning with a preambleand containing a plurality of OFDM/SC-FDM symbols. The cyclic prefixlength of OFDM/SC-FDM symbols may be shorter than those used in thecellular LTE link. The processing circuitry may be to downconvert andamplify the preambles of received D2D slots prior to analog-to-digitalconversion, wherein the preambles of received D2D slots are used forautomatic gain control (AGC). The processing circuitry may be to use thepreamble for AGC at the beginning of the data burst if the time sincethe last transmission to the second UE has been so long that the AGCsetting may be out of the range. The preamble may be a repeating signalsequence in the time domain, and each D2D slot may includes one or morereference symbols. Channel training signals or reference signals of aD2D slot may have a lower density than used in the cellular LTE link.The processing circuitry may be further to detect the preamble ofreceived D2D slots via autocorrelation. The processing circuitry may befurther to initiate a communications session with the second UE usingcarrier sense multiple access (CSMA) with respect to a D2D slot by:sensing a current D2D slot to determine if transmission activity ispresent; and, if the current D2D slot is not busy, sending a D2Dtransmission to the second UE at the start of a subsequent D2D slot. Theprocessing circuitry may be further to initiate a communications sessionwith the second UE by: if the current D2D slot is not busy, starting acountdown with a selected number; decrementing the countdown after eachnon-busy D2D slot is detected and suspending the countdown when a busyD2D slot is detected; and sending the D2D transmission to the second UEat the start of the next D2D slot after the countdown reaches zero. Thespecified number for the countdown may be randomly or pseudo-randomlyselected. A D2D slot may further includes a reservation time encoded ina control channel that specifies how many D2D slots are to beconsecutively transmitted by a transmitting device. The D2D slots may benumbered consecutively in the time and/or frequency domain. Theprocessing circuitry may be further to, when a reservation time isdetected in a D2D slot, discontinue sensing of D2D slots until thereservation time expires. The processing circuitry may be further to,when a reservation time is detected in a D2D slot, enter a sleep stateuntil the reservation time expires. The processing circuitry may befurther to transmit an indication of a transmission power level in eachD2D slot. The preamble may be a repeating signal sequence in the timedomain with a periodicity indicative of the transmission power level.The processing circuitry may further comprise a bank of correlators withdifferent correlation durations for detecting arrival of the preambleand transmission power level.

In another embodiment, a UE comprises a radio transceiver to provide anair interface for communicating with an eNB and for D2D communicationsand processing circuitry connected to the radio transceiver to: receiveallocations of time-frequency resources for D2D communications from theeNB and establish a D2D communications session with a second UE. Theprocessing circuitry may be further to transmit the indication oftransmission power level in one or more reference symbols, where aspecified reference symbol or specified sequence of reference symbolsindicates the transmission power level. The transmission power level maybe specified before actual data transmission for enabling interferenceprediction when multiple transmit power levels coexist. The processingcircuitry may be further to transmit and indication of transmissionpower level as encoded bits in a physical layer header following apreamble. The physical layer header may further comprise an indicationof the number of D2D slots that make up a transport block and are to beconsecutively sent. The processing circuitry may be further to receiveallocations of time-frequency resources for D2D communications from theeNB in response to a channel reservation request, and wherein anindication of transmission power level for D2D communications and theduration of the reservation are contained in the channel reservationrequest. The channel reservation request may be transmitted atsufficiently high power that other UEs in proximity to the device maylearn of the channel reservation and transmission power level.

In another embodiment, a UE comprises a radio transceiver to provide anair interface for communicating with an eNB and for D2D communicationsand processing circuitry connected to the radio transceiver to: receiveallocations of time-frequency resources for D2D communications from theeNB; establish a D2D communications session with a second UE, whereinD2D transmissions to and from the second UE are organized into D2D slotswith each D2D slot containing a plurality of OFDM/SC-FDM symbols, byinitiating a communications session with the second UE using carriersense multiple access (CSMA) with respect to a D2D slot by: sensing acurrent D2D slot to determine if transmission activity is present; and,if the current D2D slot is not busy, sending a D2D transmission to thesecond UE at the start of a subsequent D2D slot. The processingcircuitry may be further to initiate a communications session with thesecond UE by: if the current D2D slot is not busy, starting a countdownwith a selected number; decrementing the countdown after each non-busyD2D slot is detected and suspending the countdown when a busy D2D slotis detected; and sending the D2D transmission to the second UE at thestart of the next D2D slot after the countdown reaches zero. Thespecified number for the countdown may be randomly or pseudo-randomlyselected. A D2D slot may further include a reservation time encoded in acontrol channel that specifies how many D2D slots are to beconsecutively transmitted by a transmitting device. The processingcircuitry may be further to, when a reservation time is detected in aD2D slot, discontinue sensing of D2D slots until the reservation timeexpires. The processing circuitry may be further to, when a reservationtime is detected in a D2D slot, enter a sleep state until thereservation time expires.

The embodiments as described above may be implemented as methods foroperation and/or in various hardware configurations that may include aprocessor for executing instructions that perform the methods. Suchinstructions may be contained in a suitable storage medium from whichthey are transferred to a memory or other processor-executable medium.

The subject matter has been described in the context of an LTE network.Except where inconsistencies would arise, the subject matter could beused in other types of cellular networks with references to a UE and eNBreplaced by references to a terminal and base station, respectively.

The subject matter has been described in conjunction with the foregoingspecific embodiments. It should be appreciated that those embodimentsmay also be combined in any manner considered to be advantageous. Also,many alternatives, variations, and modifications will be apparent tothose of ordinary skill in the art. Other such alternatives, variations,and modifications are intended to fall within the scope of the followingappended claims.

The Abstract is provided to comply with 37 C.F.R. Section 1.72(b)requiring an abstract that will allow the reader to ascertain the natureand gist of the technical disclosure. It is submitted with theunderstanding that it will not be used to limit or interpret the scopeor meaning of the claims. The following claims are hereby incorporatedinto the detailed description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. An apparatus of user equipment (UE) configuredfor direct communication with one or more other UEs, the apparatuscomprising: a memory; and a processing circuitry, configured to:demodulate signaling acquired from an enhanced node B (eNB), thesignaling indicating resource configuration information for a sidelinkcommunication, the sidelink communication comprising a device-to-device(D2D) communication between UEs; modulate control information, for theD2D communication, for transmission within resources of a physical D2Dcontrol channel in accordance with a single-carrier frequency divisionmultiplexing (SC-FDM) technique; modulate data for the D2D communicationfor transmission within resources of a physical D2D shared channel, inaccordance with the SC-FDM technique; and generate a demodulationreference signal (DMRS) for transmission within resources allocated forD2D communications, wherein resource blocks for the D2D communicationare determined in accordance with a predefined hopping pattern whenfrequency hopping is enabled, and wherein the DMRS is configured fordemodulation of the physical D2D control Channel and the physical D2Dshared channel by another UE.
 2. The apparatus of claim 1 wherein theprocessing circuitry is further configured to modulate synchronizationinformation for the D2D communication for transmission by the UE, thesynchronization information based on the demodulated signaling.
 3. Theapparatus of claim 1 wherein the processing circuitry is configured todecode the signaling acquired from the eNB to determine the resourcesallocated for the D2D communication, including the resources of thephysical D2D control channel and the resources of the physical D2Dshared channel.
 4. The apparatus of claim 1 wherein the UE is configuredto include a cyclic prefix for the D2D communication to another UE, andwherein a length of the cyclic prefix for the D2D communication isdifferent than a length of a cyclic prefix used for uplink transmissionsto the eNB.
 5. An apparatus of user equipment (UE) configured for directcommunication with one or more other UE, the apparatus comprising: amemory; and a processing circuitry, configured to: demodulate signalingacquired from an enhanced node B (eNB), the signaling indicatingresource configuration information for a sidelink communication, thesidelink communication comprising a device-to-device (D2D) communicationbetween UE; modulate control information, for the D2D communication, fortransmission within resources of a physical D2D control channel inaccordance with a single-carrier frequency division multiplexing(SC-FDM) technique; modulate data for the D2D communication fortransmission within resources of a physical D2D shared channel, inaccordance with the SC-FDM technique; and generate a demodulationreference signal (DMRS) for transmission within resources allocated forD2D communications, wherein resources blocks for the D2D communicationare determined in accordance with a predefined hopping pattern whenfrequency hopping is enabled, wherein the UE is configured to include acyclic prefix for the D2D communication to another UE, wherein a lengthof the cyclic prefix for the D2D communication is different than alength of a cyclic prefix used for uplink transmission to the eNB, andwherein the length of the cyclic prefix for the D2D communication isshorter than the length of the cyclic prefix for the uplinktransmission.
 6. The apparatus of claim 1 wherein the processingcircuitry is configured to derive synchronization information fromsignals received from the eNB.
 7. The apparatus of claim 1 wherein theprocessing circuitry is configured to derive synchronization informationfrom signals received from another UE acting as a synchronizationreference for the D2D communication.
 8. The apparatus of claim 1 furthercomprising transceiver circuitry that is configurable for amulti-carrier transmission in accordance with an orthogonal frequencydivision multiplexing technique and that is configurable forsingle-carrier transmission in accordance with the SC-FDM technique. 9.The apparatus of claim 8 further comprising one or more antennas coupledto the transceiver circuitry.
 10. A non-transitory computer-readablestorage medium that stores instructions for execution by a processingcircuitry of a user equipment (UE) configured for direct communicationwith one or more other UEs, the instructions to configure the processingcircuitry to: demodulate signaling acquired from an enhanced node B(eNB), the signaling indicating resource configuration information for asidelink communication, the sidelink communication comprising adevice-to-device (D2D) communication between UEs; modulate controlinformation, for the D2D communication, for transmission withinresources of a physical D2D control channel in accordance with asingle-carrier frequency division multiplexing (SC-FDM) technique;modulate data for the D2D communication for transmission withinresources of a physical D2D shared channel, in accordance with theSC-FDM technique; and generate a demodulation reference signal (DMRS)for transmission within resources allocated for D2D communications,wherein resource blocks for the D2D communication are determined inaccordance with a predefined hopping pattern when frequency hopping isenabled, and wherein the DMRS is configured for demodulation of thephysical D2D control channel and the physical D2D shared channel byanother UE.
 11. The non-transitory computer-readable storage medium ofclaim 10 wherein the processing circuitry is further configured tomodulate synchronization information for the D2D communication fortransmission by the UE, the synchronization information based on thedemodulated signaling.
 12. The non-transitory computer-readable storagemedium of claim 10 wherein the processing circuitry is configured todecode the signaling acquired from the eNB to determine the resourcesallocated for the D2D communication, including the resources of thephysical D2D control channel and the resources of the physical D2Dshared channel.
 13. An apparatus of user equipment (UE) configured fordirect communication with one or more other UEs, the apparatuscomprising: a memory; and a processing circuitry, configured to:demodulate signaling acquired from an enhanced node B (eNB), thesignaling indicating resource configuration information for a sidelinkcommunication, the sidelink communication comprising a device-to-device(D2D) communication between UEs; demodulate control information, for theD2D communication, received within resources of a physical D2D controlchannel in accordance with a single-carrier frequency divisionmultiplexing (SC-FDM) technique; demodulate data for the D2Dcommunication received within resources of a physical D2D sharedchannel, in accordance with the SC-FDM technique; demodulate ademodulation reference signal (DMRS) received within resources allocatedfor D2D communications; and demodulate the physical D2D control channeland the physical D2D shared channel based on the demodulated DMRS;wherein resource blocks for the D2D communication are determined inaccordance with a predefined hopping pattern when frequency hopping isenabled, and wherein the DMRS is configured for demodulation of thephysical D2D control channel and the physical D2D shared channel and isreceived from another UE.
 14. The apparatus of claim 13 wherein thephysical D2D control channel and the physical D2D shared channel arereceived from another UE.
 15. The apparatus of claim 13 wherein theprocessing circuitry is configured to derive synchronization informationfrom signals received from another UE acting as a synchronizationreference for the D2D communication.